Electric discharge device



Feb. 13, 1951 w. H. TEARLT 2,541,842

ELECTRIC DISCHARGE DEVICE Filed Dec. 30, 1949 Inventor William H. Teareby fiZLQZT-Z,AJM

His Attorney mama-rears, 1951.

UNITED STATES PATENT OFFICE H 2.54am

ELECTRIC DISCHARGE DEVICE William H. TeareQBaliaton Lake, to GeneralElectric Company,

NewYork N. Y assignor a corp ration of My invention relates to improvedelectric discharge devices of the type employing an ionizable medium andparticularly to improved devices of this type employing a pool cathodeand an immersion type of starting electrode.

Electric discharge devices employing a pooltype cathode and animmersion-type starting electrode are known. In one form of such devicethat has met with considerable commercial success a starting electrodecomposed of a sintered carbide or mixture of carbides is employed incombination with a mercury pool cathode. Devices of this character havebeen widely used and have been quite successful, particularly inapplications where the substantial arc-dro of the mercury vapor, e. g.,ten or more volts, is not ob- Jectionable. In lower voltageapplications, however, this substantial arc drop has been a seriouslimitation in the use of mercury are devices. The present invention hasfor an important object, the provision of an electric discharge deviceof the above type which retains the desirable characteristics of theignitron, as the above devices are called, and at the same time operateswith a substantially lower voltage drop in the arc.

It is known that cesium vapor provides an ionizable medium through whichan arc discharge of low voltage may be maintained. Cesium vapor has beenemployed in hot cathode, electric discharge devices. Priorto myinvention. cesium has not been employed as a pool type cathode incombination with an immersion type of starting electrode; and startingelectrodes, such as the sintered carbides, mentioned above would beinoperative in the cesium tube since electrodes of this character do notoperate to initiate a cathode spot when they become wetted as they wouldin a cesium pool. Starting electrodes of this type are also attacked bythe cesium and could not be used. I have found. however, that byutilizing a dielectricstarter and preferably a ceramlo starterincombination with a pool of cesium" that a successful. pool-type of tubeutilizing an immersion starter is provided. Metals other than cesium maybe employed to advantage and.

these include alloys of cesium and potassium or cesium and sodium.Alloys of sodium potassium may also be employed. The alloys have theadvantage that they are liquid at a lower temperature than the metalsalone and may be in the liquid state at ambient temperature normallyencountered in tube applications.

In accordance with another feature of my invention the surface ofinsulates employed in the discharge devices are treated, to improvetheir 2 surface resistance characteristics when subjected to vapor ofthe cathode metal or alloy.

My invention will be better understood from a consideration of thefollowing description taken in connection with the accompanying drawingand its scope will be pointed out in the appended claims. In thedrawing, the single figure is an elevational view partially in sectionof an electric discharge device embodying my invention.

Referring now to the drawing, I have shown my invention embodied in anelectric discharge device of the metal-envelope type in which theenvelope is made up of a pair of cup-shaped memhers I and 2 which areprovided at their open ends with flanges 3 and l. The members I and 2are assembled with the flanges 3 and l in contact. These flanges arehermetically joined together in any suitable manner such as by seamwelding. The anode 5 of the device which mayto advantage be formed in ametal such as copper is supported within the envelope in insulatedrelation with respect thereto by an anode supporting conductor 6 whichis joined to a metal sleeve I by a flanged portionii. The sleeve 1 issupported from the upper end of the cup-shaped envelope member 2 bymeans of a metal sleeve 9 which is hermetically sealed to the member 2at its lower end and bonded at its upper end to an insulating sleeve l0. The lower end of the sleeve I is bonded to the upper end of theinsulating sleeve It. A suitable flexible conductor II is receivedwithin the sleeve 1 and bonded thereto to provide a suitable terminal'for the anode. The insulating sleeve In is preferably a ceramic materialand may to advantage be bonded to the metal sleeves l and 9 bythe use ofa solder metal and a metal hydride as described and claimed in copendingKelley application Serial No. 36,289, filed June 30, .1948.

and thereby initiating an arc discharge between the anode 5 and thecathode i2 i provided by a conductor II which extends into the cathodel2 and is separated therefrom by a dielectric sleeve it. As illustratedin the drawing, the sleeve II is received within a collar i5 extendingfrom the lower end of the envelope and supported therefrom. The sleeve I4 is preferably of a ceramic material such as an oxide'or silicate ofzirconium lic wool.

or an oxide of aluminum. These materials are preferred since they notonly function in accordance with the present invention to initiate acathode spot in the cesium, as will be explained in more detail at alater point in the specification, they are also very resistant to attackby the cesium. In its broader aspects, however, the present inventioncontemplates the use of any refractory dielectric material for thesleeve ll which is sui'iiciently resistant to attack by the cesium tohave a satisfactory commercial life. The dielectric sleeve I4 issuitably bonded to the sleeve '5, as by the hydride method mentionedabove, and is sealed at its lower end by a metal cap it which alsoprovides a support and terminal for the conductor iii of the startingelectrode. The conductor I3 is preferably welded to the central portionof the cap it. In the preferred embodiment illustrated, the sleeve H isof substantially larger diameter than the conductor i3 and the spacebetween these members is filled with a conducting material II which toadvantage may be a metal- The region of contact between the sleeve I4and the conductor l3 should extend above the cathode surface regardlessof variations in the cathode surface level.

I have found that in the operation of the discharge device describedabove employing a ceramic starting sleeve H and a ceramic insulatingsleeve I II that condensed cesium or alloy of the pool on the surface ofthese members thoroughly wets the surface thereof and tends to destroythe surface insulating properties of the ceramic. In the case of thesleeve In this short circuits the anode to the cathode and in the caseof the sleeve it short circuits the exposed metallic wool ll of thestarting electrode to the cathode. In accordance with another feature ofmy invention this difiiculty is eliminated by applying a thin layer ofglass to the inner surface of the sleeve l0 as shown at It and to theportion of v the starting sleeve it above the level of the cathodeliquid as shown at l9. Preferably, the glass on the sleeve of thestarting electrode is spaced. approximately 4" from the surface of thepool cathode. The glass surface may be applied by melting a powderedglass on these surfaces or by melting a suitable ring of glass intocontact with the surfaces.

It is apparent that these glas es should be reasonably resistant toattack by ce ium and for this purpose I have found that a glass havinethe following composition is satisfactory: $102-$793; Ems-18%;A12O:i-10%; Ba035%. Other glasses having reasonable resistance to attackby cesium are known and any of the e may be employed. It has been knownfor a long time that glass insulators could not be used satisfactorilyin cesium pool tubes since they were readily attacked by the cesium.This attack, however, resulted primarily from the presence of the oxideat the meta-l-to-glass seal. The use of a glass coating in the mannerdescribed above has made it possible to use the ceramic to metal sealsand at the same time to preserve the surface insulating properties ofthe glass.

While the melting point of cesium metal is 28.5 C., cesium potassium;cesium sodium or sodium potassium alloys have a lower melting point andmay be a liquid state at room tem erature. Even with the metalliccesium, suificient cesium oxide is normally present to depress themelting point below 28.5 C. and to provide a liquid pool at roomtemperature.

As will be readily understood by those skilled I in the art and as morefully described in my copending application Ber. No. 135,987, now PatentNo. 2,523,789, filed concurrently herewith, initiation of discharge in adevice of the character described above is accomplished by impressing avoltage pulse of relatively short duration between the conductor ii ofthe starting electrode and the cathode it. If the voltage is ofsuflicient magnitude, a cathode spot will be formed in the region aroundthe dielectric sleeve I 4 on the cathode surface. If the device isfilled with cesium vapor and a voltage is applied between the anode Iand the cathode it while there is a cathode spot, a discharge betweenthe anode and cathode will take place. The cesium vapor will provide anionizable medium when the temperature of the cathode is in theneighborhood of 150 C. At the time of initial starting of the device thecathode may be heated to a suitable tempertaure in the order of C. to C.to produce the required cesium vapor for initiation of the discharge. Itis preferable, however, to provide within the envelope a filling of aninert gas such as xenon, argon, crypton, neon or the like to provide anionizable medium when the temperature of the cathode is substantiallybelow that required to produce an adequate cesium vapor pressure. Theinert gas may have a pressure in the order of 5 to 100 microns at 20 C.Since the conductor I! of the starting electrode assembly iselectrically exposed to the exterior of the device above the cathodepool, it will be apparent that as soon as ionization is present a lowimpedance path in shunt with the sleeve I4 is provided. This serves toremove the voltage stress from the sleeve as soon as possible after thecathode spot is formed.

A discharge device constructed in accordance with my invention possessesthe desirable characteristics of accurate control of the initiation ofdischarge, the ability to handle currents of large magnitude and at thesame time to operate with a voltage drop in the order of 5 volts whichrenders it particularly desirable for low voltage applications.

While I have shown and described a particular embodiment of myinvention, it will be apparent to those skilled in the art that changesand modifications may be made without departing from the features of myinvention, and I, therefore, aim in the appended claims to cover allsuch changes and modifications that fall within the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric discharge device comprising an envelope, means providingan anode surface within said envelope, a pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising cesium, a starting electrode including a conductor extendinginto said pool cathode and insulated therefrom by a body of ceramicmaterial, and an inert gas filling within said envelope to facilitatestarting of an arc discharge within the device when the vapor pressureof the cesium is insufficient for that purpose.

2. An electric dischar e device comprising an envelope, means providingan anode surface within said envelope, a pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising cesium, a starting electrode including a conductor extendinginto said pool cathode and insulatedtherefrom by a body of cesiumresistant dielectric material, and an inert gas filling within saidenvelope to facilitate starting of an arc discharge within the devicewhen the vapor pressure of the cesium is insuillcient for that purpose.

3. An electric discharge device comprising an envelope, means providingan anode surface within said envelope, a pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising an alloy of metals selected from the group consisting ofcesium, sodium and potassium, a starting electrode including a conductorextending into said pool cathode and insulated therefrom by a body ofceramic material.

4. An electric discharge device comprising an envelope, means providingan anode surface within said envelope, a pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising an alloy of metals selected from the group consisting ofcesium, sodium and potassium, a starting electrode including a conductorextending into said pool cathode and insulated therefrom by a body ofcesium resistant dielectric material.

5. An electric discharge device comprising an envelope, means providingan anode surface within said envelope, 5, pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising cesium, a starting electrode including a conductor extendinginto said pool cathode and insulated therefrom by a body of ceramicmaterial, and an inert gas filling within said envelope at a pressure oflive to 100 microns to provide an ionizable medium within said envelopewhen the vapor pressure of said cesium is insufficient to supportionization.

6. An electric discharge device comprising an envelope, means providingan anode surface within said envelope, a pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising an alloy of cesium and a metal selected from the groupconsisting of sodium and potassium, a starting electrode including aconductor extending into said pool cathode and insulated therefrom by abody of ceramic material, and an inert gas filling within said envelopeat a pressure of five to one hundred microns to provide an ionizablemedium within said envelope when the vapor pressure of said cesium isinsuflicient to support ionization.

"I. An electric discharge device comprising an envelope, means providingan anode surface within said envelope, a pool cathode within saidenvelope in insulated relation with respect to said anode surface andcomprising cesium and a starting electrode including a conductorextending into said pool cathode a sleeve of ceramic material ofsubstantially larger inside diameter than said conductor surroundingsaid conductor and insulating said conductor from said pool andconducting material interposed between said conductor and the inner wallof said sleeve.

8. An electric discharge device comprising an hermetically sealedenvelope including spaced metal, parts exposed to the interior of thedevice and electrically insulated by a member of ceramic material, saiddevice including within the envelope an ionizable medium which whencondensed on the ceramic wets the surface and destroys the surfaceinsulating properties thereof and a layer of glass on the surface of theceramic member exposed to the interior of the device.

9. An electric discharge device comprising an hermetically sealedenvelope, an electrode sealed through the envelope and supported ininsulated relation therewith by a ceramic member having a surfaceexposed to the interior of the device, an ionizable medium within thedevice which when condensed onthe surface of the ceramic member wets thesurface and destroys its electrical insulating properties and a layer ofglass on the surface of a ceramic member.

10. An electric discharge device comprising a hermetically sealedenvelope, a liquid pool cathode within the envelope, a startingelectrode including a conductor sealed through the envelope wall andextending into the pool cathode, a member of ceramic materialsurrounding the conductor to insulate the electrode from the cathode,said ceramic member extending substantially above the surface of saidcathode and having an opening electrically exposing the startingconductor to the interior of the device, and a layer of glass on theexterior wall of said ceramic member in the region above the surface ofthe cathode pool to prevent the destruction of the surface insulatingproperties of the ceramic member by condensed liquid from the cathodeand the resultant shorting of the conductor and cathode.

11. An electric discharge device comprising a hermetically sealedenvelope, a liquid pool cathode within the envelope, a startingelectrode sealed through the envelope wall and extending into the poolcathode, a member of ceramic material surrounding the starting electrodeto insulate the electrode from the cathode, said ceramic memberextending substantially above the surface of said cathode, saidconductor being electrically exposed to the interior of the device abovethe .level of said cathode and a layer of glass on the exterior wall ofsaid ceramic member in the region above the surface of the cathode poolto prevent the destruction of the surface insulating properties of theceramic member by condensed liquid from the cathode.

WILMAMH.TEARE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Hull NOV. 29, 1949

